Answer:
Operation Twist is a program which is used by the FED to use the proceeds from the sale of short-term bonds to buy the long-term bonds. This is intended to put the downward pressure on the long-term yield. By buying the long-term bonds from the proceeds from short-term bills increases the demand for the bonds. Increased demand increases the price of them which makes the yield to decline as the difference between face value and the coupon or the purchase value decline.
Quantitative easing, on the other hand, is purchasing the bonds by the government which pushes up the prices of the bonds in the economy and so decreases the interest rates, a move made to make the monetary conditions easier. (C)